BEFORE 1960, rock ‘n’ roll had inevitably been seen as a rough-edged, spontaneous invention of teenagers. By that year, however, the teenage performers — and the producers and musicians they worked with — had got a little older and many were ready to try newer things. Admittedly the early ‘60s in the United States was the heyday of the idol-makers who manipulated many non-talents into the charts; but, from the more general point of view, the music was still evolving under its own steam.